To upgrade your Mystic Moon ruin, you need Mystic Moon Shards.
With each upgrade, you need more Mystic Moon Shards.
Below is a list of possible ways to gain these.
Gems
You can purchase Mystic Moon Shards using gems.
1 Mystic Moon Shard = 15 Gems
10 Mystic Moon Shards = 125 Gems
100 Mystic Moon Shards = 1,154 Gems
1000 Mystic Moon Shards = 10,000 Gems
Chest
You can purchase a chest using guild coins to have a chance at
gaining extra Mystic Moon Shards.
To purchase, click bag, click chests, click the third icon on right hand side.
The chest is called Magical Shard Box and costs 22,500 Guild Coins.
It randomly gives you 10 shards for any of the ruins or statues.
Campaign Elite Sweeps
You can sweet elite campaigns to pick up extra Mystic Moon shards.
Elite 6-1
Elite 6-2
Elite 6-3
Elite 6-4
Elite 6-5
Elite 6-6
Chests
Chest from the VIP daily clan gifts (Moonseekers city) gives Mystic Moon shards too.
VIP Daily Clan Gifts
You can collect 3 Mystic Moon shards per gift from daily VIP Clan gifts (Once you have level 25 diplomacy for this city).